1. Field of the Invention
The present invention relates to a lubrication-condition detector, a lubricant feeder, an injection molding machine including the same and a method of detecting lubrication condition.
2. Description of Related Art
There have been known injection molding machines for injecting melt of a resin or a metal into dies for molding. Many machine tools such as the injection molding machines include a driving mechanism that repeats a predetermined operation at a predetermined cycle.
In an exemplary arrangement of an injection molding machine, an injection shaft accommodated inside a cylinder is axially reciprocated to inject a molding material having been supplied into the cylinder.
Such a driving mechanism, which generally includes bearing(s) and ball screw(s), uses a lubricant for preventing frictions and rusts, cooling and the like.
A lubricant is degraded by a long time use to deteriorate the lubricity. A lubricity shortage on bearings and ball screws may cause heating, noises, vibrations or the like. If the driving is continued with the lubricity shortage, burning or the like may arise.
In order to avoid such problems, a lubricant feeder according to a known arrangement regularly feeds the lubricant in accordance with a driving time of the machine tool and the number of operations of the driving mechanism.
However, in general, not only a single driving mechanism requires the lubricant but also plural driving mechanisms may require suitable feed of the lubricant. Since such plural driving mechanism are different from one another in operation frequency and ranges of movement, a rate at which the lubricant is degraded varies depending on the driving mechanisms. Accordingly, it has been highly difficult to feed the lubricant to all the driving mechanisms without excess or shortage.
When the lubricant feed is in shortage (e.g., the lubricant feed is a small amount), the above-described problems may arise. On the other hand, when a large amount of the lubricant is fed, excessive lubricant may leak out of the driving mechanism(s) to cause pollution around the driving mechanism(s).
In view of the above problems, a grease supplier disclosed in Document 1 (JP-A-2003-176830) monitors values of electric characteristics between an outer ring and inner ring of a bearing (i.e., driving mechanism) and determines lubrication condition based on the monitored values so as to supply grease thereto.
The grease supplier according to Document 1, which supplies the grease based on the lubrication condition, can supply the grease without excess or shortage.
However, the grease supplier according to Document 1 is not intended to be applied to a driving mechanism that repeats a predetermined operation at a predetermined cycle. Thus, the grease supplier may not be able to suitably determine lubrication condition of a driving mechanism that repeats a cycle operation.
Values of electric characteristics between an outer ring and inner ring of a bearing that repeats a cycle operation are not continuous but exhibit transition as exemplarily shown in FIG. 3.
In the graph of FIG. 3, the vertical scale represents value(s) of electric characteristics while the horizontal scale represents time.
A period A shown in FIG. 3 represents changes of the value(s) of electric characteristics when the lubrication condition is favorable. Since the driving mechanism repeats a predetermined operation at a predetermined cycle (time T), a similar waveform of the electric characteristics values is repeatedly observed per time T.
In a period B, continuous driving of the driving mechanism for a long time degrades the lubricant and deteriorates the lubricity, such that the waveform of the electric characteristics values repeated per time T is gradually changed.
Then, as exemplarily shown in a period C, the waveform starts to be turbulent.
In the case described above, the grease supplier according to Document 1 determines that the lubricant is in shortage when the values of electric characteristics are out of a predetermined range. In other words, the grease supplier according to Document 1 uses only the maximum value or the minimum value in the waveform of the electric characteristics values repeated per time T so as to determine the lubrication condition.
Accordingly, for instance, when the waveform is so greatly turbulent that the lubricant may be in shortage although the minimum value or the maximum value of the electric characteristics values during time T is not greatly varied, the grease supplier according to Document 1 may not be able to suitably supply the grease.
In addition, in some exemplary cases, although the values of the electric characteristics are observed to be out of the predetermined range, the observed values may be determined to be accidental in comparison with the waveforms of preceding and subsequent cycles, such that it can be properly considered that the lubrication condition is favorable. Even in such cases, the grease supplier according to Document 1 may determine that the lubrication condition is unfavorable and supply the grease in an excessive amount.